1. Field of the Invention
The present invention relates to a combination metal gasket and a seal structure that exhibit excellent durability without exhibiting the plastic deformation even under a high compressive load.
2. Description of the Related Art
So far, in the sealing of vacuum equipment and pressure fluid conduits, rubber gaskets, resin gaskets or metal gaskets typical in O-rings are in use. Among these, for positions that are exposed to a high temperature atmosphere and necessary to be elastically rebound, metal gaskets such as so-called C-shaped rings, S-shaped rings and E-shaped rings are in use.
The E-shaped ring is disclosed in, for instance, JP-A No. 2002-5290 that is patent literature 1. The gasket that has an E-shaped cross section has overcome a problem in that in a gasket that has a so-called C-shaped cross section shape, when the sealing properties are improved the displacement follow-up performance is deteriorated; on the contrary, when the displacement follow-up performance is improved, the sealing properties are deteriorated. That is, the E-shaped gasket, in addition to exhibiting an elastic rebound force (seal load) competing against the compressive load and thereby giving excellent sealing properties, moves elastically over a wide range to exhibit a stretching force in accordance with a variation of the compressive load, resulting in enabling to obtain excellent displacement follow-up performance.
Furthermore, in JP-A No. 08-145183 that is patent literature 2, a vacuum sealing gasket is disclosed, the vacuum sealing gasket being an elastic metal structure having a V-shaped or W-shaped longitudinal cross section on a sealing surface of which a rubber film having a thickness from 0.1 μm to 0.5 mm is combined, a rubber ring being fitted in a trough portion of the elastic metal structure. According to the vacuum sealing gasket, since the elastic metal structure follows-up a non-uniform seal gap in a seal portion and a thickness of the rubber film that is combined therewith and high in the shape restorability is made thin, a gas emission quantity is small even in a very high vacuum region and the repeating usage can be realized.
Patent literature 1; JP-A No. 2002-5290 (claim 1)
Patent literature 2; JP-A No. 08-145183 (claims 1 through 3)
However, the conventional S-shaped gasket and E-shaped gasket, as shown in FIG. 7, in the case of a large compressive load P that exceeds the elastic limits of their shapes being applied, stress is concentrated on backs 61, 61 of C-shaped cross-sectional portions to result in causing the plastic deformation. At this time, there is a problem in that since the elastic rebound force cannot be demonstrated, the sealing properties cannot be obtained. In FIG. 7, reference numerals 62 and 63 denote members being sealed. Furthermore, there is another problem in that when vibrations are applied repeatedly under a compressive load close to the elastic limit, the gasket undergoes the metal fatigue, resulting in a decrease in the durability due to the fatigue and destruction. Still furthermore, in the case of pressure difference between a side of a fluid being sealed and a side of a non-fluid opposite thereto being high, since the S-shaped or E-shaped ring gasket is usually low in the tightening load, a gap is generated at a sealing portion, resulting in causing the leakage. When simply a thickness of the S-shaped or E-shaped ring gasket is increased or a hard material is used, the tightening load can be increased; however, in this case, an elastic region is remarkably narrowed. Furthermore, in a gasket in which a rubber ring is combined like in JP-A NO. 08-145183, there is a problem in that the elastic metal structure cannot be yet sufficiently complemented in the elasticity, even more, cannot be used in high temperature regions.
Accordingly, an object of the present invention is to provide a metal gasket and a seal structure that do not demonstrate the plastic deformation even under a large compressive load, cause the destruction of the gasket with difficulty even when a pressure of a fluid being sealed is high, and thus exhibits stable sealing properties.